Low-pressure arc discharge tube arrangement



April 1, 1958 .1. c. MOERKENS 2,829,311

LOW-PRESSURE ARC DISCHARGE TUBE ARRANGEMENT Filed April 24, 1955 INVENTOR JOZEF conueus, MOERKENS AGENT United States Patent-- LOW-PRESSUREARC DISCHARGE TUBE ARRANGEMENT Jozef Cornelis Moerkens, Eindhoven,Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc.,New York, N. Y., a corporation of Delaware Application April 24, 1953,Serial No. 350,807 Claims priority, application Netherlands May 15, 19524 Claims. or. 315-138) The invention relates to low-pressure arcdischarge tube arrangements without any provision for ignition switches,more particularly to fluorescent lamps comprising two activated mainelectrodes and at least one auxiliary electrode arranged Within thedischarge space on the wall of the discharge vessel, connectedelectrically within the discharge space to one of the main electrodes,insulated from the other main electrode and extending parallel to thedischarge path, and comprising in addition a rare gas-filling at apressure of a few mm.

' When a tube of the foregoing type is connected in series with asuitable stabilizing impedance to a current source of suitable voltage,a glow discharge occurs between the main electrode connected as thecathode and the end of the auxiliary electrode insulated therefrom,

which, emanating from the cathode, travels along the auxiliary electrodeonto the main electrode electrically connected thereto. As soon as oneof the main electrodes assumes emission temperature, the glow dischargeis converted into an arc discharge between the main electrodes.

It has been observed that the life of such tubes is a voltage whichexceeds the supply voltage, and since the discharge current of this tubetraverses a portion of the first inductance, an increased voltage isalso applied across the other tube connected in series with the entirefirst inductance.

The portion of the first inductance which is common to both tubecircuits and the impedance ofthe auxiliary reactance are preferablyproportioned such that the starting voltage of the tube connected inseries with the capacitor exceeds the starting voltage of theothertube..

At a supply voltage of approximately 220 volts, the number of turns ofthe first inductance which are included in both tube circuits may befrom 10 to 20% of the total number of turns thereof.

The invention will now be described with reference to the accompanyingdrawing, wherein the single figure is a schematic diagram of anembodiment of the circuit arrangement of the present invention.

Referring now to the figure, there are provided two low-pressure arc.discharge tubes 1 and 2, for example,

about 120 cms. in length, having an internal diameter" of approximately35 mms. and containing an argon filling' at a pressure of approximately3 mms. in addition to asrnall supply of mercury. The tubes 1 and 2, eachof which has the inner surface of its discharge vessel coated with afluorescent layer (not shown), each comprise two main electrodes 11, 12and 21, 22 respectively,

which are activated by means of barium-strontium compounds, and anauxiliary electrode 13 and 23, respectively. 'The auxiliary electrodesconsist of a mixture of. graphite and glazing and are applied to theinner-surface of the tube wall in the form of an approximately -3detrimentally affected by the number of tube-starting operations. At arated power supply voltage of 220 volts the tube can be started onlyseveral hundreds of times on an average, and if the tube is kept in useeach time for a short period only, the result is an insufiiciently shortlife.

, According to the invention, it has been found that the number of timesthe tube can be ignited is increased as the period of time between thetube being energized and the arc discharge being efifected is decreased.It has also been found that at an effective A. C. voltage ofapproximately 240 volts or more, the said period of time is reduced to asmall fraction of a second, and hence the number of times the tube canbe started'is greatly increased. Moreover, at effective A. C. voltagesexceeding approximately 280 volts, no appreciable supplementary 240 to280 volts. One of the tubes is connected in series with an inductance tothe A. C. supply of the system and the other tube is connected to thissupply in series with a second inductance, a capacitor having areactance which exceeds that of the second inductance, and a portion ofthe first inductance. The reactance more remote from the firstinductance, i. e., the second inductance or the capacitor, is connectedto the current supply in series with an auxiliary reactance which takesa current of the opposite sense.

The provision of the auxiliary reactance ensures that the tube connectedin series with the capacitor ignites at mm. wide strip runningsubstantially the whole length of the tube and which are connected toone of the main electrodes and exhibit a resistance of approximately .20to 30 ohms per cm. If required, each tube may include a second auxiliaryelectrode connected to the other main electrode.

Connected across the terminals 7 and 8 of an A. C.;

supply of 220 volts, 50 cycles per second, are the tube 1 through afirst inductance or choke 3 and the tube 2 through a capacitor 4, asecond inductance or choke- 5 and a portion 6 of the choke 3. Anauxiliary inductanceor choke 9 is connected in parallel with'the tube2,'

the choke 5 and the portion 6 of the choke 3, and in series with thecapacitor 4.

The choke 3 contains, for example, 1480 turns, and at a voltage of 175volts across its ends carries a current of 0.42 ampere, therebyexhibiting an impedance of approximately 420 ohms. The portion 6comprises 235 turns and, hence, approximately 16% of the total number ofturns of the choke 3.

The capacitor 4 has a capacitance of, for example, 5 microfarads, thatis to say, an impedance of approximately 635 ohms.

At a voltage of 100 volts, the choke 5 carries a current of 0.44 ampereso that its impedance is approximately 230 ohms.

At a voltage of 270 volts, the auxiliary choke 9 carries a current of0.07 ampere and at a voltage of 180 volts it carries a current of 0.03ampere, so that in these conditions its impedance is approximately 3850and 6000 ohms, respectively. The voltage-ampere product deciding emenThe phase-leading discharge current of the tube 2 passing through theportion 6 of the choke 3 produces a voltage of 255 volts across the tube1, whereupon this tube,

also attains the are discharge condition almost at once.

All this ensues so quickly that the glow discharge periods.

of the tubes can o'nlybe observed at a greatly reduced voltage.

The number of turns of the portion of the choke 6 7 2strikes. has 220volts applied to it and might ignite at this voltage,,is thus preventedfrom being kept in suspense in the glow discharge condition for anexcessively long period.

Under normaloperating conditions, the voltage across the tube 1 isapproximately 110 volts .at a tube current o'fl'approximatelyOAZ ampere;the'voltage across the tube 2 in this condition is approximately 110volts at a tube current of approximately 0.44 ampere. In this case, thecurrent passing through the auxiliary choke 9 is approximately 0.03ampere, that passing through the capacitor 4 approximately 0.475 ampere,and the total current supplied by the current source approximately 0.45ampere.

The wattless currents or apparent power of the tube circuitsiare ofopposite sense, so that the power factor ofith'e arrangement has a highvalue. The stroboscopic effect ofth'e device is low, since the darkperiods of the tubes do not occur. simultaneously.

With the invention, the life of the tubes is several thousands of tubestarting operations.

1 While I have described myinvention in connection with specificembodiments and applications, other modifications thereofwill'be readilyapparent to those skilled inlthi's'art without departing from the spiritand the scope offtlie invention as defined in the appended claims.

' What is claimed is:

l. A circuit arrangement comprising a pair of .low pressurearc-dischargev tubes each having a pair of activated main electrodes andan auxiliary electrode, a source of potential at a given alternatingfrequency, a firstinductance 'in series with said source and one of saidtubes, asecond inductance and the other of said tubes connected inseries circuit arrangernent, means for connecting said.

series circuit in series with a portion of 'said first 'inductance, acapacitative reactance connectedin series with said series circuitarrangement and said source, said capacitative reactance having-a'valueexceeding the value of said second inductive reactance at saidfrequency, and an auxiliary inductive reactance connected in series withsaid source and said capacitative reactance.

.-2. An arrangement as claimed in claim 1, in which said .portion ofsaidfirst inductance and the impedance of the-auxiliary reactance areproportioned such that the starting voltage of said other tube exceedsthe "starting voltage ofsaid one tube.

' 3. An arrangement as claimed in claim 2, in which the number of theturns of said portion of the-first 'inductance is from 10 to 20% of thetotal number of turns of the first inductance.

4. A circuit arrangement including a pair of low pres sure arc-dischargetubes each having a pair of activated main .electrodes, a pair ofterminals connected respectively to said pair of main electrodes, anauxiliary electrode connected to one of said main electrodes andextending through the tube to the vicinity of but insulated from saidother main electrode, and a rare gas-filling at a pressure of a few mm.;said arrangement further comprising a source of potential at a givenalternating frequency, a first inductance in series with said source andI one of said tubes, a second inductive reactance connected to oneterminal of the other-of said tubes and in seriesv with a portion onlyof said first inductance, a capacitative reactance connected to theother terminal of said other tube and in series with said secondinductive reactance and said source, said capacitative reactanceexceeding the value of said second inductive reactance at said givenfrequency, and an auxiliary inductive reactance connected to said otherterminal of said other tube and in series with said source and saidcapacitative reactance.

References Cited in the file of this patent UNITED STATES PATENTS2,025,471 Osborne Dec. '24, 1935 2,301,671 Abadie Nov. 10, 19422,314,311 Karash Mar. 16, 1943 2,504,549 Lemmers Apr. 18, 1950 2,518,767Freeman Aug. 15, 1950 Hall Nov. 10, 1953

